Abstract/Description

Maize stackburn, the discoloration of stored maize as a direct result of heat build-up in the interior of stacks, has emerged as a significant threat to food security in sub-Saharan Africa during the last decade. The problem affects white and yellow...

Notes

Maize stackburn, the discoloration of stored maize as a direct result of heat build-up in the interior of stacks, has emerged as a significant threat to food security in sub-Saharan Africa during the last decade. The problem affects white and yellow maize, (local and imported) and is unpredictable. When affected (for a period over 100 days) the grain embryo and kernel become discoloured, turning to a dark brown colour. The result is wastage and downgrading of thousands of tonnes of grain every year.
To meet the urgency of the situation, the EU funded a collaborative research project starting in 1993, to determine the precise causes of the heat build-up in stacks. Organizations involved are the Natural Resources Institute (NRI) UK the University of Zimbabwe and the Grain Marketing Board (GMB) Zimbabwe, the University of Ghana and the Ghana Grains Development Corporation and the Instituto Investigaçao de Cientifica Tropical (CEFA) Portugal. The factors being investigated as possible causes include insect pest development, mould growth, type of sack material used, biochemical changes within the grains and the interaction of all these factors. Field trials in Ghana and Zimbabwe will determine the pattern of the heat build-up that causes the discoloration.
A new stacking method, designed to dissipate heat from the core of large stacks, is being perfected by the GMB. A series of channels is built along the width and length of standard stacks which also form vertical channels at their intersections. Remote instrumentation, to measure temperature and moisture content changes within one of the stacks, was provided by the UK Overseas Development Administration. Apart from the introduction of channels, the GMB stacks are built to standard requirements: outdoors on poles at the base (two layers at right angles or pallets to provide an air gap), covered during the rainy season and aired in good weather, and regularly fumigated. Space lost to channels built into the stack is calculated to be less than 10%. With training, semiskilled 'stack builders' can construct a ventilated stack in the same time taken to building an unventilated stack.
The ventilated stack in Zimbabwe is the first attempt to introduce a practical solution to the problem of stackburn. The results of the trial are eagerly awaited by large-scale storers of grain in several countries.
The authors would welcome correspondence from workers experiencing stackburn and who would like further information about the problem and measures being introduced to prevent it.
Tim Donaldon, Peter Tyler
Natural Resources Institute
Chatham Maritime
Central Avenue
Kent ME4 4TB, UK
Atonia Maia
Instituto de Investigacao Cientifica
Tropical/CEFA
Trav. Conde da Ribeira 9
1300 Lisboa, PORTUGAL
Stanley Nosenga, Noah Kutukwa, Ronia Tanyongana
Grain Marketing Board
PO Box 8014
Causeway
Harare, ZIMBABWE